1. Field of the Invention
The present invention relates to a fixing structure for fixing an optical element, a laser scanning apparatus including the fixing structure for fixing the optical element, an image forming apparatus including the laser scanning apparatus, and a method for fixing the optical element in the fixing structure for fixing the optical element.
2. Description of Related Art
Heretofore, an image forming apparatus, such as a laser printer and a digital copier, is equipped with a laser scanning apparatus which scans a photoreceptor with laser light emitted from a semiconductor-laser light source held by a light source holder.
Recently, expected performance for the laser scanning apparatus has become higher, and also performance of the optical element and attaching accuracy of the optical element has tended to become higher. An elongated optical element is hard to handle because the elongated optical element is easily deformed when attached and fixed to an optical element holder. In a reflective optical system, compared with a transmission optical system, an error of the attaching position and the deformation of the optical element have a large influence on an irradiation position of the laser light on the photoreceptor. Therefore, in the reflective optical system, it is very difficult to ensure accuracy of the irradiation position of the laser light on the photoreceptor even when an environment changes.
Accordingly, there has been a demand for a method for attaching the optical element to the optical element holder by which method the optical element is not subject to stress and misalignment due to the environmental change after the attachment is reduced.
As conventional attaching method of the optical element, Japanese Patent Application Laid-open No. 11-281865 discloses a configuration where an optical element is positioned by positioning pins whose tips have radiuses (or radiuses of curvature) same as one another.
Japanese Patent Application Laid-open No. 2007-65500 discloses a configuration where an optical element is sandwiched between positioning pins and elastic members whose tip shapes are same as that of the surface of the optical element.
Japanese Patent Application Laid-open No. 2008-3373 discloses a configuration where a whole adhesive surface of an optical element is bonded and fixed to a base using an ultraviolet curing adhesive.
Japanese Patent Application Laid-open No. 2003-207733 discloses a configuration where an optical element is bonded and fixed to a base using an ultraviolet curing adhesive after the position of the optical element is adjusted.
Japanese Patent No. 4744125 disclose a conventional optical element fixing structure including: elastic members which press an elongated optical element by an elastic force; and holding members and adjustment members, each of which is paired with each of the elastic members, and which support the elongated optical element against a pressing force of the elastic member. In the optical element fixing structure, the holding members fixed to a holder member or integrated with the holder member support both end portions in a longitudinal direction of the elongated optical element, and the adjustment members held by the holder member is movable in a direction of the pressing force of the elastic member. According to the technique disclosed in this document, a strain amount of the elongated optical element can be adjusted and thereby beam position performance such as a scanning line deviation can be corrected, which deviation occurs due to a form error and/or an assembly error of the elongated optical element or other optical components whose form is deviated away from an ideal state.
However, since the technique disclosed in Japanese Patent Application Laid-open No. 11-281865 fixes the optical element using the positioning pins whose tips have radiuses same as one another, there is a problem that the optical element cannot be positioned in a circumferential direction and rotation about an optical axis of the optical element cannot be suppressed.
Moreover, since the technique disclosed in Japanese Patent Application Laid-open No. 2007-65500 fixes the optical element using the positioning pins whose tip shapes are same as that of the surface of the optical element, there is a problem that a base point from which stretching in a longitudinal direction of the optical element occurs due to a length difference in linear expansion cannot be defined and misalignment of the optical element occurs in the case that expansion and contraction are repeated due to the environmental change.
Furthermore, since the technique disclosed in Japanese Patent Application Laid-open No. 2008-3373 bonds and fixes the whole adhesive surface of the optical element to the base using the ultraviolet curing adhesive, there is a problem that when a linear expansion coefficient of the optical element is different from that of the base, the optical element is deformed due to a temperature change and thereby a formed image is degraded.
Moreover, since the technique disclosed in Japanese Patent Application Laid-open No. 2003-207733 bonds and fixes the optical element using the ultraviolet curing adhesive after the position of the optical element is adjusted without providing a fixing member for temporarily fixing the optical member, there is a possibility that misalignment of the optical element occurs due to expansion/contraction of the ultraviolet curing adhesive.
Furthermore, according to the optical element fixing structure disclosed in Japanese Patent No. 4744125, the correction of the beam position performance makes the optical element distorted to produce stress. This stress changes due to repetition of the environmental change, which results in a problem in that the beam position performance is changed from a time point of an initial adjustment.
In addition, in the case that an optical element is a reflective optical system such as a mirror, when the optical element is distorted for correcting the beam position performance, there is encountered a problem that beam imaging performance such as a beam diameter and a field curvature are largely degraded.